I have many Model Entities like
class Employee {
private Integer id;
private String name;
}
class Address {
private Integer id;
private String address;
}
and many more..
Can we map all Entities together in single hbm xml mapping file?
I know it might not be good practice. but Still can we do it? If yes then how ?
Yes. It is possible to use a single mapping file.
Something like this:
<hibernate-mapping>
<class name="Employee" table="employee">
<id name="id" type="java.lang.Integer">
<column name="id"/>
<generator class="native"/>
</id>
<property name="name" type="java.lang.String">
<column name="name"/>
</property>
</class>
<class name="Address" table="address">
<id name="id" type="java.lang.Integer">
<column name="id"/>
<generator class="native"/>
</id>
<property name="address" type="java.lang.String">
<column name="address"></column>
</property>
</class>
</hibernate-mapping>
Yes you can do this, the dtd (http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd) allows multiple class elements in hibernate-mapping:
<!ELEMENT hibernate-mapping (
...
(class|subclass|joined-subclass|union-subclass)*,
...
)>
Even the documentation (http://docs.jboss.org/hibernate/orm/4.3/manual/en-US/html/ch05.html#mapping-declaration, second code block) maps as an example a Cat and a Dog class in the same file.
Related
I have two objets like:
public class Object1 implements Serializable {
protected Integer id; // This is the PK in the xml mapping
protected Integer otherId;
}
public class Object2 implements Serializable {
protected Integer id; // This is the PK in the xml mapping
protected Set<Object1> object1List; // I want to relate this set against the "otherId" attribute
}
And I have this hibernate XML mappings:
<class name="Object1" table="Object1Table">
<id name="id" type="java.lang.Integer">
<column name="id" />
<generator class="identity" />
</id>
<property name="otherId" type="java.lang.Integer">
<column name="other_id"></column>
</property>
</class>
<class name="Object2" table="Object2Table">
<id name="id" type="java.lang.Integer">
<column name="id" />
<generator class="identity" />
</id>
<set name="object1List" table="Object1Table" lazy="false" fetch="join" >
<key column="other_id" /> // This is not working
<one-to-many class="Object1" />
</set>
</class>
But I don't know how to relate the "set" mapping against the "other_id" attribute, it only works against the PK "id" of the "Object1" table.
Does anyone know how to solve this situation?
I think you need to mark the <set as inverse. Like crizzis mentioned, you'd be better off if you use the annotation model. A lot more people can help you with the annotation model. Apart from that, the HBM XML mapping will be replaced with the JPA orm.xml mapping at some point, so I wouldn't use that approach anymore.
I am a new bie to the world of hibernate could you please advise , I was going through one to one relationship in Hibernate,
As per my analysis , one to one hibernate relationships can be established by three ways..
1)Through Join concept
2)Same primary key in both the tables
3)Primary key and foriegn key relationship in both the tables
Please advise , the above three ways to achieve the one to one mapping is correct or I am missing something then please advise, and also please advise that the below hbm mapping files that I am using are correct one.if not then please advise.
1) Through Join concept :-
One way to achieve to one to one relationship is by joining concept , following xml is being used for that
<hibernate-mapping>
<class name="mypack.Person" table="person21">
<id name="personId" type="int">
<generator class="increment">
</generator>
</id>
<property name="name"/>
<join table="personAddress">
<key column="personId"/>
<many-to-one name="address" class="mypack.Address" column="addressId" unique="true" cascade="all"/>
</join>
</class>
<class name="mypack.Address" table="address21">
<id name="id" column="addressId" type="int">
<generator class="increment"/>
</id>
<property name="city"/>
<property name="state"/>
</class>
</hibernate-mapping>
2) Same primary key in both the tables :-
Using same primary key in both the tables , following hbm is being used for that
<class name="mypack.Address" table="address31">
<id name="id" column="addressId" type="int">
<generator class="increment"/>
</id>
<property name="city"/>
<property name="state"/>
</class>
<class name="mypack.Person" table="person31">
<id name="personId" type="int">
<generator class="foreign">
<param name="property">address</param>
</generator>
</id>
<property name="name"/>
<one-to-one name="address" class="mypack.Address"/>
</class>
</hibernate-mapping>
3)Primary key and foriegn key relationship in both the tables :-
Primary key in one table and foriegn key in another table. below is the hbm for this
<hibernate-mapping>
<class name="mypack.Person">
<id name="personId" type="int">
<generator class="increment"/>
</id>
<property name="name"/>
<many-to-one name="address" class="mypack.Address" column="addressId" unique="true" cascade="all"/>
</class>
<class name="mypack.Address">
<id name="id" column="addressId" type="int">
<generator class="increment"/>
</id>
<property name="city"/>
<property name="state"/>
</class>
</hibernate-mapping>
folks please advise.
I really think that join table is overkill here for a one-to-one mapping. For the other 2 solutions, please take a look at the following Hibernate documentation, everything is explained : http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/mapping.html#mapping-declaration-onetoone.
For your second mapping (primary key association), both entities need to define a one-to-one mapping and one side of the relation also needs to specify the attribute constrained="true".
This is how I would write your second mapping :
<class name="mypack.Person" table="PERSONS">
<id name="id" type="int" column="PERSON_ID">
<generator class="increment"/>
</id>
<property name="name" type="string" column="NAME"/>
<one-to-one name="address" class="mypack.Address" cascade="all"/>
</class>
<class name="mypack.Address" table="ADDRESSES">
<id name="id" type="int" column="ADDRESS_ID">
<generator class="foreign">
<param name="property">address</param>
</generator>
</id>
<property name="city" type="string" column="CITY"/>
<property name="state" type="string" column="STATE"/>
<one-to-one name="person" class="mypack.Person" constrained="true"/>
</class>
I have a table Project with fields
ID
PROJECT_BASELINE_ATTRIBUTES_ID (FK for table PROJECT_BASELINE_ATTR)
This table has the following mapping
<hibernate-mapping package="com.initech.db.model">
<class name="com.initech.db.model.Project" table="PROJECT">
<id name="id" column="id" type="java.lang.Long">
<meta attribute="use-in-tostring">true</meta>
<generator class="sequence">
<param name="sequence">PROJECT_ID_SEQ</param>
</generator>
</id>
<many-to-one name="projectBaselineAttributes" column="PROJECT_BASELINE_ATTRIBUTES_ID" class="com.initech.db.model.ProjectBaselineAttributes" cascade="all" not-null="true">
<meta attribute="use-in-tostring">true</meta>
</many-to-one>^
</class>
</hibernate-mapping>
The respective Project.java class has the fields
private Long id;
private ProjectBaselineAttributes projectBaselineAttributes;
Furthermore, I have a table PROJECT_BASELINE_ATTR, containing the field
ID
The Hibernate mapping:
<hibernate-mapping package="com.initech.db.model">
<class name="com.initech.db.model.ProjectBaselineAttributes" table="PROJECT_BASELINE_ATTR">
<id name="id" column="id" type="java.lang.Long">
<generator class="sequence">
<param name="sequence">PRO_BASE_ATTR_ID_SEQ</param>
</generator>
</id>
<set name="projects" table="PROJECT" inverse="true" lazy="true" fetch="select">
<key>
<column name="PROJECT_BASELINE_ATTRIBUTES_ID" precision="22" scale="0" not-null="true" />
</key>
<one-to-many class="com.initech.db.model.Project" />
</set>
</class>
</hibernate-mapping>
The respective ProjectBaselineAttributes.java class has the fields
private Long id;
private Set projects = new HashSet();
The current mapping is not ideal, as the relationship between the two tables is actually one-to-one, but in the ProjectBaselineAttributes I have a set of Projects, even though there is always one Projet for one ProjectBaseLineattributes. What should the mapping look like for ProjectBaselineAttributes so that I can get the associated Project "singularly", i.e. so that the class ProjectBaselineAttributes.java would look like this:
private Long id;
private Project project;
Here's the section of the Hibernate documentation which details how to map such a bidirectional one-to-one association using a foreign key.
<class name="Person">
<id name="id" column="personId">
<generator class="native"/>
</id>
<many-to-one name="address"
column="addressId"
unique="true"
not-null="true"/>
</class>
<class name="Address">
<id name="id" column="addressId">
<generator class="native"/>
</id>
<one-to-one name="person"
property-ref="address"/>
</class>
create table Person ( personId bigint not null primary key, addressId bigint not null unique )
create table Address ( addressId bigint not null primary key )
You can try the below mappings as told in this example.
In the parent bean,
<one-to-one name="one2oneSubA1" class="com.manu.hibernate.mappings.domain.ASub1" cascade="all"
property-ref="parent"/>
In the child bean,
<many-to-one name="parent"
class="com.manu.hibernate.mappings.domain.AMain" column="a_id"
unique="true" cascade="save-update" />
I'm sure there must be thousands of examples demonstrating this association but I can't seem to find one anywhere.
I have a one-many relationship from Parent-Child and a many-one relationship from Child-Parent:
class Parent {
private Long id;
private String name;
private List<Child> children;
}
class Child {
private Long id;
private String name;
private Parent parent;
}
I'm expecting to end up with 2 tables that look as follows:
Parent
- id : bigint
- name : varchar
Child
- id : bigint
- parent_id : bigint
- sequence : bigint
- name : varchar
Have I got the right idea? If so does anyone know what I need to put in my mapping file so that when a parent is deleted so too are it's children.
Thanks in advance.
James
Found the solution in the end although I don't understand why I need insert="false" and update="false":
<hibernate-mapping>
<class name="foo.Parent" table="Parent">
<id name="id" type="int" column="id">
<generator class="native" />
</id>
<property name="name" type="java.lang.String" column="name" length="50" />
<list name="children" cascade="all">
<key column="parent_id" />
<index column="sequence" />
<one-to-many class="foo.Child" />
</list>
</class>
<class name="foo.Child" table="Child">
<id name="id" type="int" column="id">
<generator class="native" />
</id>
<property name="name" type="java.lang.String" column="name" length="50" />
<many-to-one name="parent" class="foo.Parent" column="parent_id" insert="false" update="false" />
</class>
</hibernate-mapping>
I have 2 tables, one table is
City Table ( int id, string name)
and my another table is
Distance table(int id,int cityId (FK city),int neighbourId(FK city))
I want to use Hibernate but I can't establish a relationship between these tables in Hibernate.
what about something like
<class name="City" table="CITIES">
<id name="id" type="integer">
<generator class="native" />
</id>
<property name="name" />
<set name="neighbours" table="DISTANCES">
<key column="city_id" />
<many-to-one name="neighbour" class="City" />
</set>
</class>
didn't test it though.
Ok, I can see any problem to do it normally.
<class name="City" table="CITY">
<id name="id" type="integer">
<generator class="native" />
</id>
<property name="name" />
</class>
<class name="Distance" table="DISTANCE">
<id name="id" type="integer">
<generator class="native" />
</id>
<many-to-one name="city" column="cityId" class="City"/>
<many-to-one name="neighbour" column="neighbourId" class="City"/>
</class>
didn't test it neither.